The technology of mobile communication base station antenna is developing rapidly. At first, ordinary directional antennas and omni-directional antennas were mainly used domestically. Nowadays, electronically tunable antenna is more and more popular. The so-called electronically tunable antenna refers to base station antenna of which the electrical downtilt angle is adjustable. The principle of electrical downtilt is, by changing the phase of conformal linear array antenna element, to change the amplitude of vertical component and horizontal component of the field strength and change the field strength of synthetic component, thereby making the vertical directivity pattern of the antenna tilt downward. Since the field strength of the antenna in all directions simultaneously increase and decrease, it is guaranteed that the shape of the antenna directivity pattern basically remains unchanged after changing the tilt angle, thereby shortening the coverage distance of the main lobe direction and reducing the coverage area for the entire pattern in service cell sector but without producing interference. Practice has proved that when the downward angle of the electronically tunable antenna changes between 1°-5°, the directivity pattern of the electronically tunable antenna is roughly the same as that of mechanical antenna; when the downward angle changes between 5°-10°, the directivity pattern of the electronically tunable antenna is slightly improved from that of the mechanical antenna; when the downward angle changes between 10°-15°, the directivity pattern of the electronically tunable antenna is much different from that of the mechanical antenna; when the downward angle of the electronically tunable antenna exceeds 15°, the directivity pattern of the electronically tunable antenna is significantly different from that of the mechanical antenna, and in this case, the shape of the antenna pattern changes little, the coverage distance in the main lobe direction shortens significantly and entire antenna directivity pattern is within base station sectors. Thus, increasing the downward angle can shorten the coverage area of the sectors without producing interference. Such directivity pattern is what we need. Therefore, using electronically tunable antenna can decrease call loss and reduce interference. In addition, electronically tunable antenna allows system to adjust downtilt angle of the vertical directivity pattern and monitor adjustment effect in real time without the system going down. The stepping accuracy (0.1°) for adjusting the tilt angle is high, thereby fine adjustment for the network can be achieved.
The above characteristics of the electronically tunable antenna require that to achieve precise adjustment for the downtilt angle, idealized settings for mechanical tilt angle of antenna element must be guaranteed. Otherwise, idealized directivity pattern cannot be obtained by just adjusting the electrical downtilt angle. However, the changes of initial construction and mounting location of the station, which is caused by that the existing electronically tunable antenna encounters typhoon or mounting fixtures aging, cannot be found timely. When new base station sites are constructed, deviation occurs to the antenna mounting position. And adjustment for horizontal orientation and mechanical tilt angle cannot be controlled remotely. All these defects are due to that effective monitoring for horizontal orientation angle and mechanical tilt angle of the electronically tunable antenna cannot be made and working staff cannot obtain corresponding angle information timely, thereby resulting in the inconvenience for the construction and maintenance of electronically tunable antenna.